diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index 30d069c..c0bcf17 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -4898,7 +4898,11 @@
       if (this_rd_stats.rate != INT_MAX) {
         const int ext_tx_set = get_ext_tx_set(
             mbmi->min_tx_size, bsize, is_inter, cm->reduced_tx_set_used);
-        const TX_SIZE square_tx_size = txsize_sqr_map[mbmi->min_tx_size];
+        TX_SIZE square_tx_size = txsize_sqr_map[mbmi->min_tx_size];
+#if CONFIG_TX64X64
+        // For TX_64X64, use TX_32X32 to lookup cost
+        if (square_tx_size == TX_64X64) square_tx_size = TX_32X32;
+#endif  // CONFIG_TX64X64
         this_rd_stats.rate +=
             x->inter_tx_type_costs[ext_tx_set][square_tx_size][mbmi->tx_type];
         this_rd_stats.rate -=